The invention relates to an arrangement for the continuous heat setting of yarns, which are guided by means of transport belts into, and then out of, a heat setting chamber using superheated steam. At least one central mast is provided which is equipped with several circulating transport belts, arranged in a polygonal pattern in cross section. At least one yarn is wound around the central mast and the transport belts in controlled loops.
An arrangement of this kind is disclosed in U.S. Pat. No. 4,513,514. In the case of this known arrangement, the guide pulleys of the transport belts are arranged so far away from the heat setting chamber that the transport belts cool to under 100.degree. Celsius before they enter the heat setting chamber again. The superheated steam in the heat setting chamber can then partly condense onto the transport belts causing damp spots on the transported yarn which then cannot be heat set without imperfections occurring. When a yarn which has not been heat set properly is later dyed, it can result in undesirable color differences or variations.
It is known from the published German patent application 16 10 940 that the complete transport belts including all the guide pulleys and the winding flyer which winds the yarn around the transport belts are arranged inside the heat setting chamber. The disadvantage of this arrangement is that the relevant bearings of the guide pulleys are also heated, which has an adverse effect on their lifetime. It is further known that the transport belts running inside the heat setting chamber are subdivided into several belt sections, which are arranged out of line with respect to each other, so that when the yarn is being transferred from one belt section to the next, the yarn always lies on a different place in order to prevent pressure marks occurring.
It is an object of the invention in the case of an arrangement of the above mentioned type to prevent an unacceptably high level of condensation on the transport belts.
This object is achieved according to preferred embodiments of the invention in that the transport belts are themselves each subdivided into belt sections which are arranged consecutively at transfer points, the transfer points being arranged directly upstream and/or downstream of the heat setting chamber.
As the central mast projects further out of the heat setting chamber on the outgoing side than on the ingoing side, it is frequently sufficient according to certain preferred embodiments of the invention to place a transfer point of two belt sections downstream of the heat setting chamber. The criterion must be hereby observed however that the temperature of the transport belts passing through the heat setting chamber does not fall below 100.degree. Celsius when they leave the heat setting chamber. This criterion is usually met when at least 85% of the travel paths of the transport belts that pass through the heat setting chamber are inside the heat setting chamber. Further preferred embodiments are contemplated for the case of particularly critical yarns, where transfer points are arranged both upstream and downstream of the heat setting chamber.
It is advantageous according to certain preferred embodiments of the invention to provide yarn guiding elements at the transfer points, which arrangement prevents tangling of the yarn loops.
In especially preferred embodiments, double guide pulleys, preferably rubber coated ones, are provided at the transfer points. This results in a simplification of the drive, as the belt sections reaching a transfer point drive the double guide pulleys and therefore also the following belt sections. It is thereby useful when the guide pulley of each double guide pulley on the side towards the central mast is arranged for each successive belt section.
In an advantageous development of certain preferred embodiments of the invention it is provided that at the transfer point, which precedes the heat setting chamber, the guide pulleys have differently sized diameters. The relevant guide pulley of the following belt section preferably has the larger diameter. The transported yarn is, on the one hand, kept taut so that bends or kinks do not occur; on the other hand, the transfer density is reduced dye to the faster speed of the following belt section, which results in a better penetration due to the working climate. This is in particular the case with single high twist yarns or with so-called "SIRO".TM. spun yarn, which is not evened out in its ply torque. In the case of folded "BCF".TM. yarns it is not necessary to have different pulley diameters. On the contrary, in this case the following belt sections are even let run over smaller diameters so that the yarn can shrink unhindered. The pulley diameters do not need to be different either downstream of the heat setting chamber, as here the heat setting process is already completed.
In a further development of the invention, the cross section circumference of the transport belts, which are arranged in a polygonal pattern, is changeable. On the one hand, the support surfaces of the yarn can be changed, which results in avoidance of pressure marks, while on the other hand the shrinking behavior of the heat set yarn is taken into consideration. A longitudinal rail or a tension wire or similar device can hereby be provided for enlarging the cross section circumference, so that the yarns do not hang through between two transport belts. This is particularly advisable in the case of polyester yarns.
Inside the heat setting chamber it is convenient according to certain preferred embodiments of the invention to have the yarn loops carried only by two upper transport belts. The lower transport belts are guided by suitable guiding means away from the loops and slightly towards the inside so that the loops can hang freely downwards. Experience has shown that pressure marks which hamper the heat setting are thus avoided. However, the loops must be guided by all transport belts again before reaching the next transfer point.
The loops, hanging freely downwards, are advantageously stretched outwards by rust-free tension wires or similar devices according to certain preferred embodiments. These tension wires should be capable of being adjusted in their positions to adapt to shrinkage.
As the round transport belts which are usually used can rotate around their own axis, which can lead to random orientation of the loops, it is intended in a further development of the invention to use round, but softer transport belts. These are pressed flat during operation and are therefore incapable of rotating.
In order to reduce even further the condensation build-up in the heat setting chamber, the transport belts can be made as wire cords according to certain preferred embodiments of the invention. These have the advantage that they practically cannot absorb any dampness internally.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings.